Utility knives which incorporate a retractable, replaceable razor blade have been popular in many applications for years. There are deficiencies, however, in the prior art designs which limit their usefulness in certain applications. For example, in the roofing trade it is generally necessary for the roofer to carry two such utility knives. One knife is equipped with a straight razor blade for cutting felt paper and the like, while the other knife is equipped with a hooked blade for cutting shingles and the like which have a granulated surface. Neither of these knives are well adapted for cutting the other type of material, therefore it is necessary for the roofer to carry both types of knives.
Carrying two knives, however, is inconvenient, especially when working on a roof. Whenever it is necessary to switch knives, the user must retract the first blade and stow the first knife, take out the second knife and extend the second blade. This is extremely inconvenient during applications where use of both knives in alternating succession is routinely required.
There have been attempts in the prior art to solve this problem. For example, U.S. Pat. No. 5,093,994 to Karas discloses a double-ended utility knife. This knife, however, still exhibits most of the problems encountered with using two separate knives. To switch blades, the knife must be turned around, the first blade must be retracted and the second blade must be extended. Turning the knife around is generally a two-handed operation.
There is therefore a need in the prior art for a utility knife that allows use of two different blades without requiring the cumbersome manipulations required by prior art knives during blade changes. The present invention is directed toward meeting this need.